Fish and Fisheries in Estuaries. Группа авторов

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Gilchristella aestuaria, a serial spawner, spawns in response to riverine input into an estuary (Strydom & Whitfield 2000), suggesting a range of triggers for spawning in estuarine species.

      A recent synthesis focused on reproductive strategies and mechanisms, emphasising energy acquisition and allocation to spawning (McBride et al. 2015). Some species, especially large taxa such as Acipenseridae, that spawn in estuaries or their tributaries essentially are capital spawners, but individuals may not spawn every year, a strategy to maintain reproductive fitness (McBride et al. 2015). Differences in spawning strategies and processes of estuarine and estuary‐associated fishes span the known spawning alternatives in fishes. Adults may maintain flexible processes for energy acquisition and allocation to reproduction, sometimes prioritising their own nutritional condition over that of egg production to maximise reproductive value (McBride et al. 2015). The batch‐spawning engraulid Anchoa mitchilli presents an example of this strategy in Florida estuaries (Peebles et al. 1996).

      Fecundity also varies with female size. As for most bony fishes, fecundities of estuarine fishes increase rapidly with female weight. For example, fecundity increases >18‐fold from 170 000 to 3 100 000 in the moronid Morone saxatilis of 2.8–36.8 kg, respectively (Mansueti 1961, Goodyear 1985) and tenfold (12 000 to 108 000) for the autumn‐spawning Baltic clupeid Clupea harengus membras of body mass 25–70 g, respectively. Individuals of similar age may have different fecundities. For example, in three‐year‐old C. h. membras, fecundity varied from 11 100 to 73 300 eggs (Arula et al. 2012b). For the serial‐spawning engraulid Anchoa mitchilli, batch fecundities range from 500 to 2000, and total fecundity can reach 50 000 eggs in an 80‐day spawning season for an adult of average mass 1.5 g wet weight (Zastrow et al. 1991).

      Anadromy is unusual for an engraulid, for example Coilia nasus, which migrates from coastal bays, e.g. from Ariake Bay (Japan) into the Chikugo River estuary where it spawns (Suzuki et al. 2014). Small resident fish species with low fecundity often have parental care, for example gobiids, fundulids, atherinids and blennioids (Hastings & Petersen 2010, Able & Fahay 2010). In many regions, numerous estuaries, including large and complex systems (e.g. Baltic Sea, Chesapeake Bay, San Francisco Bay Estuary, Puget Sound) afford opportunity for variability in individual behaviours (portfolio effect) of spawning stock components (contingents) and variability in spawning patterns that promote sustainability of populations. Salmonids and moronids may best represent this strategy amongst estuary‐dependent species (Secor 2015, Levings 2016). There is value in maintaining a population structure that conserves old females (see Section 3.4.1.2) in many marine and estuarine fishes (e.g. Berkeley et al. 2004). Older and larger females including estuarine species such as the moronid Morone saxatilis have greatly elevated fecundities (Gervasi et al. 2019). Conserving their egg production is a tool that managers can utilise to sustain high spawning levels and high probabilities of recruitment success.

       3.2.1.2 Early‐life stages and nurseries

      Ontogeny of estuarine fishes begins at fertilisation and continues after hatching, usually involving dramatic changes in morphology, biomass, sensory systems and behaviour, including swimming performance up to the juvenile stage, and thus colonisation of estuarine nurseries (Webb 1999, Fuiman & Werner 2002, Miller & Kendall 2009, Pavlov & Emel’yanova 2016). These early‐life history transitions occur during the stages of smallest size, fastest growth and highest mortality (Houde 1989a, 2016, Pepin 1991, 2016). The complex ontogenetic transitions in early life contribute to factors generating recruitment variability (see Section 3.3) in marine and estuarine fishes (Houde 2016).

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